In northern climates during winter months, aircraft which are either parked on the ground overnight or which are on the ground during severe winter weather frequently accumulate snow or ice on the airfoil surfaces. It is thus necessary to remove this material prior to takeoff and such removal has been the subject of a variety of deicing equipment in the prior art. The typical approach is to apply deicing compositions to aircraft in wintery weather before takeoff to deice them and to prevent ice from forming for a certain period (the so-called “hold-over time”). This goal is frequently achieved with mixtures of water and ethylene glycol or water and propylene glycol
The most popular equipment to apply the deicing mixtures are self-contained trucks having an extendible and maneuverable boom mounted thereon and a tank containing the deicing mixture. The truck typically includes a self-contained heater that heats the glycol-water mixture to 160 to 190 degrees Fahrenheit. The heated deicing fluid is then pumped through a hose to the end of the boom where the operator directs a stream of the heated deicing fluid mixture from a nozzle onto the aircraft. This procedure removes the snow and/or ice and provides a coating of glycol which largely prevents further formation of the freezing substance during the hold-over time. This deicing procedure normally takes place on the tarmac just prior to the plane's departure after which the aircraft's normal internal electrical deicing systems are employed.
It is known to provide “glycol proportioning panels,” as they are known in the art, that mix water and pure ethylene or propylene glycol and provide the mixture to the trucks that in turn spray it onto the aircraft. Most of these known proportioning panels are large, ungainly, expensive and offer limited mixing functionality.
For example, one disadvantage of these known proportioning systems is that the desired ratio of glycol to water is typically limited to only three or four settings. However, to minimize glycol waste and to optimize the mixture for a given weather condition, more selections of glycol mixtures are desirable. Another disadvantage to presently available glycol proportioning panels is that the systems are housed in a building that may be hundreds of feet from where the truck that sprays the mix onto the aircraft is loaded. The mixture is piped over this distance. The distance between the main unit and the location where the effluent is being dispensed can create a communication problem between the operator of the panel who is located in the building, and the personnel who are loading the truck, who are outside and several hundred feet away.
Another disadvantage of known proportioning systems is that they employ variable speed or frequency pumps to proportion the percentages of glycol and water. In addition to creating more process variables to be monitored, the variable speed pumps can be undesirably slow.
Systems relying on multiport computer controlled valves to mix glycol and water are also known. For example, U.S. Pat. No. 4,842,005 (Hope et al.) discloses a glycol proportioning station wherein water is pumped by a pump and its flow rate measured by a flow meter. Glycol is pumped through another pump and through a multi-port valve, which has multiple ports of different sizes that are pneumatically opened or closed in response to pre-programmed signals from a controller that is coupled to the multiport valve. In use, the water flow rate is sensed and the flow of glycol is controlled by the multi-port digital valve, which opens and closes any number of ten possible elements, or parts, to accommodate the required flow.
It is also known in the art to use refractometers with glycol mixing systems for aircraft. For example, U.S. Pat. No. 4,986,497 to Susko discloses a deicing system in which a refractometer is used to monitor the mixed fluid and adjust flow of the glycol and water lines as necessary. Separate supply lines provide controlled flows of water and glycol to a wye-connection point. Each supply line has its own pump and throttling valve to control flow, as directed by a microprocessor. The system includes a heat exchanger into which fluid is recycled until the glycol mix reaches the desired temperature and until the refractive index read by a refractometer has reached the set point. The refractometer output signal indicates whether the refractive index is at, below, or above the set point. If below the set point, the microprocessor adjusts a valve on the glycol line to add glycol to the mix; if above the set point the microprocessor adjusts the valve on the water line to add water to the mix. Once the correct temperature and refractive index are recognized at the microprocessor, a valve is opened on the effluent line and the mixture is delivered.
U.S. Pat. No. 4,275,593 (Thornton-Trump) discloses an aircraft deicing system which includes a specific gravity meter that displays the glycol percentage to an operator positioned in a basket and a lever to adjust the glycol percentage in the effluent. By adjusting the lever, the operator may vary the amount of pure glycol fed into the mixture line and thereby adjust the glycol percentage in the effluent.
In summary, known glycol proportioning panels can be expensive, slow and inflexible. What is needed is a glycol proportioning panel that addresses these drawbacks.